Geochemistry and detrital zircon U–Pb–Hf isotopic data reveal the provenance and tectonic setting of the Xujiahe Formation

The depositional age, provenance and tectonic setting of the Xujiahe Formation have been studied, but remain intensely debated. In this study, we focus on the second segment of the Xujiahe Formation (T₃x₂) as a research object. Several sandstone samples from three sections were collected for stratigraphic, geochemical and detrital zircon analyses. Stratigraphic assemblage and features of the three sections indicate a braided river delta depositional setting, and detrital zircon U-Pb dating constrains a Late Triassic depositional age. Whole-rock geochemistry suggests that the sandstones exhibit a low degree of palaeo-weathering and primarily derived from upper crustal felsic rocks. Detrital zircons within these sandstones display uniform age peaks at intervals of 2000-1800 Ma and 500-200 Ma, with similar Hf isotopic compositions compared to those of detrital and magmatic zircons from the South Qinling Block. Taken together, these zircon age spectra and Hf isotopic signatures is determined to be indicate a mixed clastic provenance, with contributions from both the Qinling Orogenic Belt and the Yangtze Block. The clastic particle composition and whole-rock geochemistry indicate that the T₃x₂ was deposited in a passive margin tectonic setting, located within a braided river delta fed by several NE-SW-oriented paleo-rivers.